PET and SPECT Studies in Anxiety Disorders

Neuroimaging studies using PET and SPECT to evaluate neurofunctional differences between patients with anxiety- and stress-related disorders and healthy controls were reviewed. At rest, patients with social anxiety disorder display increased serotonin synthesis rate and upregulated serotonin transporter expression, whereas studies targeting dopamine have yielded mixed results. Posttraumatic stress disorder is associated with a compromised benzodiazepine receptor function. In panic disorder, both benzodiazepine receptors and serotonergic (5-hydroxytryptamine 1A (5HT1A)) receptors are downregulated. Across the anxiety disorders, there is downregulation of both benzodiazepine and 5HT1A receptors. Symptom provocation studies, where regional cerebral blood flow is measured, support that activity in the brain’s fear circuit is altered with increased reactivity in the amygdala, the midbrain, and possibly also the insular cortex, whereas activity in emotion-regulating areas in the prefrontal cortex such as the subgenual anterior cingulate cortex and the orbitofrontal cortex is compromised in the symptomatic state, predominantly in phobic disorders. Some studies demonstrate a coupling between individual differences in neurotransmission and fear network activity. Treatment studies suggest that reductions of neural activity in the amygdala may be a final common pathway for successful therapeutic interventions, thereby linking neurotransmission to plasticity in the core fear network of the brain.